In this age of environmental awareness, the wine industry is frequently tuned in to environmentally-friendly alternatives to the status-quo. For example, wineries have been known to recycle their wastes for animal feed, fertilizer, or even pharmaceuticals, in addition to reevaluating how their wines are distributed to customers. One side of the wine business that is starting to garner more attention is the packaging aspect. Wine is not only packaged in glass bottles, but also in plastic bags, plastic bottles, and even cans.
Studies and speculation have shown, however, that the type of packaging used may influence the overall quality of the wine, which ultimately relates to the gas exchange between the wine and the atmosphere through the packaging. The oxidation of wine, while important to the overall character of the wine at certain rates, may cause a loss of aromatic quality, the degradation of anthocyanins and tannins, and the appearance of a brown precipitate if too much oxygen is present.
In recent years, a particular type of plastic has been developed to potentially help reduce the amount of oxidation in wines caused by poor packaging materials. PET, otherwise known as polyethylene terephthalate, belongs to the polyester family, and has been developed for preservation of foods and beverages (sodas, juices, water, and now wine). Chemically, PET is a combination of ethylene glycol and terephthalic acid, which form a polymer chain. This chain is then broken down into small pellets, then heat applied to create a liquid which may then be formed into any desired shape. Advantages to this type of material are cited as being transparent, low cost, and strength. As a result of this technology, PET has been considered a potential acceptable replacement for glass, available in both single-layer and multi-layer forms.
The PET multi-layer form was developed in an attempt to improve the gas barrier properties of the container, and consists of a three layer structure of PET – Gas Barrier Resin – PET, or a five layer structure of PET – Gas Barrier Resin – PET – Gas Barrier Resin – PET. The gas barrier resin could be created using many compounds, with one example being an ethylene-vinyl alcohol copolymer and MXD6 nylon. One potential environmental concern with the multi-layered PET containers is that the present of the polymers in the different layers make recycling more difficult and more expensive. Boxed wine (i.e. Bag in Box®) uses similar technologies as PET, with multiple layers as described above. To protect the bag, a cardboard box is employed. Some studies have shown that PET bottles are capable of storing a wine up to 7 months, and are successful in slowing down the transfer of oxygen that would otherwise cause wine quality decay.
The study reviewed today, which is currently available only in online form until the publication comes out in January 2012, aimed to study the decay of quality in both white and red wines in different packaging types (glass bottles, PET multi-layer bottles, PET mono-layer bottles, and Bag in Box®) and different volumes (18.5cL and 75cL for bottles, and 300cL for Bag in a Box®).
The wines sampled were both red and white Bordeaux blends from the 2008 vintage. All bottling occurred via standard approved methods, and a screw cap was the chosen closure.
For the packaging, glass bottles, mono-layer PET (0.3mm thickness), multi-layer PET (0.4mm thickness), and Bag in Box® were used.
All wine samples were stored upright at 20 degC for 18 months.
Oxygen levels were measured using a chemical electrode oxygen Probe. Carbon dioxide levels were measured using the multiple expansion method. The following standard enological parameters were also measured: titratable acidity, volatile acidity, alcohol content, pH, microbiological characteristics, color characteristics, and sulfur dioxide.
Thiols were measured using gas chromatography and mass spectrometry.
For each treatment (i.e. each wine in each packaging type), samples were collected and analyzed just after bottling, and then again at 3, 6, 9, 12, and 18 months.
Sensory analysis of the wines occurred just after bottling, in addition to after 6, 12, and 18 months of aging. The panel consisted of 25 experts (researchers and PhD students of the faculty of enology at the Université de Bordeaux). Analysis took place in a standard tasting room with private booths, with wines assessed at 20oC (smell and taste). For white wines, the descriptors analyzed were limpidity, color intensity, sauvignon character, and oxidative and reduction evolutions. For red wines, the descriptors analyzed were color intensity, evolution of the color, fruity character, oxidative evolution, reduction, astringency, and bitterness. All attributes were scored on a scale from 0-5.
- The initial concentration of oxygen was 0.73mg/L
- For glass bottles and multi-layer PET (75cL), the oxygen content decreased quickly in the first three months, then remained stable and very low.
- For multi-layer PET (18.5cL) and Bag in Box®, the oxygen content was around 0.5mg/L.
- For mono-layer PET, the oxygen content was high around 1mg/L for the 75cL bottle and 2.5mg/L for the 18.5cL bottle after 12 months.
o The mono-layer PET bottle allowed oxygen to transfer into the bottle easily, and oxidized the white wine.
o Bag in Box® and the 18.5cL multi-layer PET bottle displayed oxygen transfer at a rate not as high as the mono-layer PET bottle, however still significant and could alter the sensory characteristics of the wine.
o Glass and the 75cL multi-layer PET bottles were the best barriers to oxygen for white wines.
- The initial concentration of carbon dioxide was 0.9mg/L.
- Bag in Box® and the 18.5cL mono-layer PET bottle had a low CO2 concentration of <0.5g/L.
- For all other packaging types, the CO2 concentration ranged from 0.5g/L to 1g/L.
- CO2 concentrations were relatively constant for glass bottles and the multi-layer PET bottles.
- Note: if free SO2 drops below 10mg/L, white wine will be subject to oxidation and increased browning.
- Glass bottles and multi-layer PET bottles contained over 10mg/L free SO2 after 12 months of storage.
- The other packaging types had free SO2 levels ranging from 3 to 7mg/L.
- Note: a decrease in SO2 levels will accelerate the oxidation of a white wine and change the color hue.
- The 18.5cL mono-layer PET bottles resulted in clearly oxidized wine after 12 months in storage (OD420 value of 0.155).
- Wine from both the 75cL mono-layer PET bottles and the 18.5 multi-layer PET bottles had OD420 values reaching 0.120, which indicates oxidation.
- For all other packaging types, there was no sign of oxidation and wine color appeared normal after 18 months of aging.
Volatile Compounds & Oxidation Markers:
- 3-sulfanylhexan-1-ol decreased in all packaging types after 6 months of aging.
- Glass bottles tended to preserve 3-sulfanylhexan-1-ol levels better than the other packaging types.
- Choice of packaging influenced the dissolved oxygen level in the bottles and also the redox potential of the wine.
- There was an increase in oxidation markers:
o Levels of methional, phenylacetaldehyde, and sotolon were found from highest to lowest in the 18.5 mono-layer PET, 75cL mono-layer PET, Bag in Box®, 18.5cL multi-layer PET, and 75cL multi-layer PET bottles.
o With these packaging types, oxidation markers were found to be above their perception thresholds.
- Only aging in the 75cL glass bottles appeared to keep the wine free from oxidation markers.
- Sensory analysis indicated differences in sensory attributes depending upon which type of packaging was used.
o After 6 months, sauvignon character and color intensity was altered in the mono-layer PET, 18.5cL multi-layer PET, and Bag in Box® bottles. This same result was found at 12 and 18 months (and included all mono- and multi-layer bottle types).
- White wine sensory quality is highly influenced by packaging type, and is noticeable by 6 months of aging.
- Only Bag in Box® showed increased levels of dissolved oxygen.
- All other packaging types showed normal levels of dissolved oxygen for red wine.
- The initial level of CO2 after bottling was 0.9g/L.
- There was a linear decrease of CO2 in the glass and multi-layer PET bottles over time.
o Since CO2 cannot permeate through glass, this decrease was due to gas transfer through the screw cap closure.
- The CO2 content was higher in glass bottles than all other packaging types, and was still at acceptable levels after 18 months of aging.
- For Bag in Box®, the CO2 levels quickly decreased in the first three months of aging, however remained stable through the rest of the experiment (0.5g/L).
- There were decreases in the SO2 levels of wine in all packaging types, though the decrease was less for the glass bottles.
- SO2 levels in all packaging (except the glass bottles) was 10mg/L after 18 months of aging (this value is low).
- The color of the red wines were not influenced by the packaging type.
- There were no differences in any of the sensory attributes for any of the red wines, regardless of packaging type.
Overall, I thought the results of this study were very interesting and potentially important for finding alternative packaging for wine that is both environmental friendly and able to preserve the quality of the wine. It seems as though PET bottles (particularly mono-layered PET bottles) were the less effective in preserving the quality of white wines, as a result of rapid oxidation. The sensory analysis also showed marked decreases in wine quality of bottles created with any packaging material other than glass. I believe based on these results, it’s safe to say that the standard glass bottle is still the best vesicle for storing white wines for over 6 months of time.
The twist in this study, to me, came with the analysis of the red wines. According to the results of this study, no matter what type of packaging used, there were no degrading effects on the overall quality of the red wine. A glass bottle? A plastic bottle? A Bag in Box®? Based on what was found in this study, it doesn’t matter; the wine should taste just fine! Perhaps I’m just naïve, but that blew my mind a little bit!
Of course, more research needs to be done on more varietals of wine, to confirm if all white wines are sensitive to packaging type and all reds unfazed. All in all, I found the results of this study very interesting—what I expected for whites, but totally out of left field for the reds!
What do you all think about this? I’d love to hear your thoughts! Please feel free to comment below!
Source: Ghidossi, R., Poupot, C., Thibon, C., Pons, A., Darriet, P., Riquier, L., De Revel, G., Mietton Peuchot, M. 2012. The influence of packaging on wine conservation. Food Control 23: 302-311.
I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!